1. Field of the Invention
The present invention relates to a simultaneous ignition system for an automobile and, more particularly, to an actual ignition timing detecting device for use with the simultaneous ignition system.
2. Description of the Prior Art
One of the important factors for determining the performance of an engine is the timing for the ignition timing of each cylinder. In order that the engine may operate efficiently, the explosive force of the combustion of the fuel has to be concentrated as it is transmitted to the piston. For this purpose, ignition of the fuel generally is intended to take place as the piston moves to its position closest to the corresponding ignition plug so that the fuel is sufficiently compressed. As a practical matter, however, the ignition is often conducted immediately before or after the piston moves to its position closest to the ignition plug, as a consequence of the period from the ignition time to the time of actual combustion of the fuel, the regulation of the exhaust emission control or the like. In either event, nevertheless, the ignition timing has to be strictly set.
In the case of the maintenance of an automobile, therefore, in which the engine is to be adjusted, the ignition timing is adjusted. For this purpose, the ignition timing has to be detected.
Before entering into the description of the preferred embodiment, the prior art will be described in more detail with reference to the accompanying drawings.
FIG. 1 is a circuit diagram showing one example of an ignition system according to the prior art. Reference numeral 1 indicates a power source; numeral 2 an ignition coil; numeral 3 a contact point; numeral 4 a capacitor; numeral 5 a distributor; numeral 6 the ignition plug of a first cylinder; and numeral 7 the ignition plug of a second cylinder.
FIG. 2 is a waveform chart illustrating the ignition pulses which are to be applied to the respective ignition plugs shown in FIG. 1. These ignition pulses are indicated at such reference letters as correspond to those of FIG. 1.
In this ignition system of the prior art, when the contact point 3 is repetively opened and closed, the capacitor 4 charges and discharges the current coming from the power source 1 so that positive pulses are generated at the primary coil L.sub.1 of the ignition coil 2 in response to those charging and discharging operations. The secondary coil L.sub.2 of the ignition coil 2 has a sufficiently larger number of such windings than the primary coil L.sub.1 and they are turned in the opposite direction. As a result, the secondary coil L.sub.2 generates higher voltage negative pulses by induction from the positive pulses generated at the primary coil L.sub.1. These high pulses generated by the secondary coil L.sub.2 are applied to the distributor 5 by which they are alternately distributed to the ignition plugs 6 and 7. One train of the pulses thus distributed is applied as the ignition pulses (a) of the first cylinder (although not shown) to the ignition plug 6, whereas the other train is applied as the ignition pulses (b) of the second cylinder (although not shown) to the ignition plug 7 so that the first and second cylinders are alternately ignited.
In the case of the engine equipped with the ignition system thus far described, in order to detect the ignition timing of the respective cylinders, it is sufficient to directly detect the ignition pulses (a) and (b) by means of a sensor.
Another form of two-cylinder engine is the so-called "simultaneous ignition engine" which is equipped with an ignition system of a construction simplified by omitting the distributor.
FIG. 3 is a circuit diagram which shows the above-specified ignition system and in which the parts corresponding to those of FIG. 1 are indicated by identical reference characters. FIG. 4 is a waveform chart which illustrates the ignition pulses of the ignition system of FIG. 3 and in which the respective pulses are indicated at reference letters corresponding to those of FIG. 3.
In this ignition system, the secondary coil L.sub.2 of the ignition coil 2 is grounded through the ignition plugs 6 and 7 so that the pulses generated between both its terminals are applied as the ignition pulses to the ignition plugs 6 and 7. As a result, the ignition plug 6 of the first cylinder is supplied with the positive ignition pulses (a), whereas the ignition plug 7 of the second cylinder is supplied with the negative ignition pulses (b).
Here, in the simultaneous ignition engine equipped with the ignition system shown in FIG. 3, while one cylinder is in a fuel-compressed stroke, the other cylinder is in an exhaust stroke. Even if the cylinders have their respective ignition plugs 6 and 7 simultaneously supplied with the ignition pulses, therefore, the one cylinder in the fuel-compressed state is actually ignited (which state will be shortly be referred to as the "actual ignition"), whereas the other cylinder in the exhaust state is not ignited (which state will be shortly referred to as the "misfire").
Thus, the first and second cylinders alternately repeat the actual ignition and the misfire when they are supplied with the ignition pulse so that when one of them is actually ignited the other is misfired.
Consequently, when the ignition pulses (a) and (b) are applied to the ignition plugs 6 and 7 of the first and second cylinders, one train of alternate pulses a.sub.1 of the ignition pulses (a) will ensure the actual ignition, and the other train of alternate pulses a.sub.2 of the same will invite the misfire. Likewise, one train of alternate pulses b.sub.1 of the other ignition pulses (b) will ensure the actual ignition, and the other train of alternate pulses b.sub.2 of the same will invite the misfire. As has been described with reference to FIG. 1, therefore, even if the respective ignition pulses (a) and (b) are detected, the pulses indicative of the timing of the misfire (which pulses will be shortly referred to as the "misfire pulses") are detected in addition to the pulses indicative of the timing of the actual ignition (which pulses will be shortly referred to as the "actual ignition pulses"), thus making it difficult to detect the actual ignition timings of the respective cylinders by conventional techniques.